1. Field of the Invention
The present invention relates generally to mechanical press machines and, more particularly, to a press bearing lubrication system that provides both hydrostatic and hydrodynamic bearing support at press wrist pins and other journal bearings characterized, for example, by oscillatory motion, relatively little rotation, and/or slow rotational speeds.
2. Description of the Related Art
Mechanical presses of the type performing industrial activity such as stamping and drawing operations have a conventional configuration including a frame with a crown and bed portion and a slide supported within the frame for reciprocating movement toward and away from the bed. A crankshaft rotatably disposed within the crown is arranged in driving connection with the slide using a connecting arm assembly. A flywheel assembly rotatably driven by a drive mechanism is selectively connectable with the crankshaft for driving rotation thereof, utilizing a clutch/brake combination to make the driving connection. These mechanical presses are used in a wide variety of workpiece operations employing a large selection of die sets, with the press machine varying substantially in size and available tonnage depending upon the intended use.
The primary source for stored mechanical energy in mechanical presses is the flywheel, which is conventionally located between the main drive motor and the clutch. The flywheel and its associated bearing are mounted on either the driveshaft, crankshaft, or the press frame by use of a quill. The main drive motor replenishes the energy lost from the flywheel during press stamping operations when the clutch couples the flywheel to the press driven parts. During engagement of the clutch, the flywheel drops in speed as the press driven parts are brought up to press running speed. The flywheel rotates in unison with the engaged clutch while the flywheel bearings have no relative rotation, except for the case of a quill arrangement whereby relative rotation is always present.
One of the critical demands in mechanical presses concerns providing adequate lubrication to the system parts to safeguard their structural integrity, promote durability, and avoid premature device failure. Efforts aimed at addressing this problem have focused on developing bearing arrangements that adequately support the principal rotary components throughout their operating cycle, namely the flywheel and crankshaft. However, what has been overlooked by such efforts, and consequently absent from the accompanying press design work, is the need to provide similar bearing protection at other press machine sites which, while not representing principal sources or recipients of work-related rotational energy, nevertheless exhibit relative motion between press parts that necessarily invokes a lubricating requirement. Examples of such machine sites include wrist pins and other journal bearings where there exists relatively little rotation, oscillation, and/or slow rotational speeds.
One conventional approach aimed at providing bearing support to these secondary motion sites proposes to create a hydrodynamic effect between the bearing surfaces of the associated devices. Generating such hydrodynamic activity requires a sufficient amount of relative rotation between the devices to mobilize or activate the oil film injected into the clearance space. For components such as wrist pins, however, developing a lubricating system that relies exclusively upon adequate relative rotation to produce the needed bearing support is not a complete or satisfactory solution. Accordingly, despite the availability of hydrodynamic assistance, problems still attend such press machine sites because of their dependence upon an operating condition, namely sufficient relative rotation, that does not manifest to any suitable degree.
A bearing support system based solely on hydrodynamic activity is ineffective in lubricating devices experiencing a low order of rotational or sliding motion. These devices are therefore typically characterized by high wear rates and sometimes premature failure of the bearing due to the minimal or non-existent hydrodynamic effect which otherwise is intended to accommodate the sliding motion occurring between the bearing surfaces. In terms of power requirements, the absence of adequate lubrication means that a relatively high torque is needed to rotate the bearings due to large frictional forces caused by the bearing surfaces sliding across each other. A larger drive system is therefore required due to the reduced efficiencies in power conversion. The elevated torquing action is accompanied by related increases in the thermal energy of the lubricating area, raising the operating temperature of the bearing and causing the oil viscosity to decrease, thereby reducing the load-carrying capacity of the bearing.
Bearing support limited to hydrodynamic activity still presents certain difficulties even if the rotational speeds are sufficient to create the intended hydrodynamic effect. In particular, as the devices commence their operation from a static condition and appreciable hydrodynamic activity appears, a "lift-off" effect occurs in which the bearing surfaces yield to an displacing pressure generated by the oil film as it undergoes hydrodynamic activity. This lift-off of the bearing surfaces causes a change in position of the crankshaft, pins, and linkages, resulting in a change in the press ram position at the bottom of each stroke relative to when the press is in a static condition. This ram displacement must be taken into account when installing the ram tooling or otherwise poor part quality and damaged tooling may result.